Yes, you can update the styles of a document to match the attached
template. Open the document that should be updated. On the Tools menu,
click Templates and Add-Ins. Click the "Automatically update document
styles" option to select it, and click OK.

Note that if you revisit the dialog box, you'll find that the option
is still selected, which may not be what you want. In fact, for
documents containing numbered paragraphs, it might be a bad idea to
keep "Automatically update document styles" checked.

You can update a document's styles from the template. Styles do _not_
include margins or headers and footers. You could have the contents of your
headers and footers be AutoText fields, drawing their content from your
template.

You update the styles through the Tools > Templates and Add-Ins dialog by
checking the box to update styles from the template. Note, it is almost
always best to leave this box unchecked, which in your case would mean going
back to the dialog and unchecking the box after you've done an update. One
reason for leaving this box unchecked is that if you send the document to
another computer with the box checked, your styles would update from the
recipient's normal.dot template, probably ruining your formatting.

Probably the simplest way to update a document to match changes in the
template is to create a new document based on the template and paste the
content from your old document into the new one. Then close the old document
and save the new one to the same name and folder.

Thanks for your help, I think I'll just have to get my page layout right
first time, though the formatting tip may come in handy.